A semiconductor laser typically comprises a body of semiconductor material having opposed reflective end faces and having an active layer positioned between two cladding regions of opposite conductivity. Various laser structures have been developed to enhance particular operating characteristics. For example, buried heterostructure (BH) lasers, such as the buried crescent (BC) laser, achieve a low threshold current by index guiding, thus reducing junction temperature rise and consequently allowing higher temperature operation. A BC laser typically comprises a semiconductor body including a substrate having a buffer layer of a first conductivity type, a first blocking layer of a second conductivity type overlying the buffer layer and a second blocking layer of the first conductivity type overlying the first blocking layer. A V-shaped groove is formed through the blocking layers and into the buffer layer in a longitudinal direction, the direction perpendicular to the end faces. A first cladding region of the first conductivity type is positioned in the groove. A semiconductor layer overlies the second blocking layer and is typically discontinuous at the edge of the groove, forming a crescent-shaped active region overlying the first cladding region and having a thickness which varies in the lateral direction, the direction in the plane of the layers and perpendicular to the groove. A second cladding region of the second conductivity type fills the groove and overlies the semiconductor blocking layer. A capping layer of the second conductivity type overlies the second cladding region.
Other lasers such as the distributed feedback (DFB) laser provide a single wavelength output which is stable with temperature, time, output power, and modulation rate. A DFB laser typically comprises an active layer positioned between two planar cladding regions. Periodic corrugations comprising a plurality of elements which are parallel in the lateral direction, are located in the plane of the layers either above or below the active layer. The width of the period between elements determines the wavelength emitted. These corrugations provide spatial variations in the refractive index producing optical feedback thus eliminating the requirement of reflective end faces as in the BH or BC laser.
Combinations of the BH and DFB lasers typically position the active layer such that it overlies the planar DFB grating. It would be desirable to have an alternative laser structure incorporating the characteristics of a BC and DFB laser.